Diisocyanates which are liquid at room temperature have numerous advantages over solid diisocyanates. Diisocyanates which are liquid at room temperature, such as toluene diisocyanate or hexamethylene diisocyanate, are, as a rule, physiologically harmful because of their high vapor pressure. For this reason, various attempts have been made to start with diisocyanates that are solid at room temperature and convert these into the liquid form.
The most commercially important diisocyanates which are solid at room temperature are 4,4'-diphenylmethane diisocyanate and the 2,4'-isomer thereof, which melt at 39.degree. C. and 34.5.degree. C., respectively.
Numerous patents have issued relating to the liquification of diphenylmethane diisocyanate. See, for example, U.S. Pat. Nos. 3,152,162; 3,384,653; 3,394,165; 3,449,256; 3,640,966; 3,641,093; 3,674,828; 3,701,796; 3,883,571; 4,014,935; 4,055,548; 4,088,665; 4,031,026; 4,102,833; 4,115,429; 4,118,411; 4,154,752; 4,177,205; 4,229,347; 4,261,852; 4,321,333; and 4,332,742.
It is an object of this invention to provide improved organic isocyanates which are liquid at room temperature. A further object of this invention is to provide organic isocyanates which remain liquid even on prolonged storage at low temperatures. Still another object of this invention is to provide an improved process for preparing liquid organic isocyanates.